In Project 23, we used simple linear regression to investigate whether it rains more in Tacoma than in Seattle or Portland. Now investigate this question in the broader sense of: it rains more in a city if the mean difference in annual rainfall is greater than 0, the difference in annual rainfall being the annual rainfall of that city minus the annual rainfall of the other city. With this interpretation of “raining more”, compare:

Portland and Seattle rainfall.

Portland and Tacoma rainfall.

Seattle and Tacoma rainfall.

Background on the data set

This data set gives annual precipitation totals for Portland (OR), Tacoma (WA),
and Seattle (WA) for the years 1966-2006, precipitation being defined as: "Any form
of water particles-liquid or solid-that falls from the atmosphere and reaches the
ground."